I do not understand the rules behind having "se" in a sentence. Does it not make sense without it in this example? Where I am trying to learn this does not explain the rule.
This is because the verb
ir can be a pronominal verb. In such cases, the verb is conjugated together with a personal form.
In this case in particular it is use to emphasize the action the subject is making (going to a restaurant). The non-pronominal way is also correct, but you don't emphasize the action:
Él va al restaurante
Pronominal Verbs can be used to reinforce the involvement of the subject to the action of the verb. A reflexive pronoun can be added to a transitive verb to emphasize the entire action.